Process for Auto-Testing a Fully Discharged Battery, Such as Double-Layer Capacitor Battery, and Circuit for Doing the Same

ABSTRACT

A process for performing an auto-test of a fully discharged battery of an electronic appliance including a battery charger, said process involving the steps of :
         performing an initialization phase;   charging said battery with a predetermined constant current during a predefined period allowing stabilization of said current (Icurrent);   detecting the voltage of said battery after said predefined period, said battery being still in charge;   testing whether said sensed voltage is comprised within a predetermined range of threshold values (V1, V2), and   reporting a battery failure when said sensed value is outside said range.       

     The invention is particularly adapted to the auto-test of a backup battery made of Electric double layer capacitors or any fully discharged backup battery.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/819,377, filed Feb. 27, 2013, which is the National Stage ofInternational Application No. PCT/EP2011/004374, filed Aug. 31, 2011,which claims priority to EP Patent Application No. 10368040.1, filedOct. 15, 2010 and EP Patent Application No. 10368035.1, filed Aug. 31,2010, the disclosures of each of which are incorporated herein byreference in their entirety.

TECHNICAL FIELD

The present invention relates to the field of electronics circuits andmore particularly to a process for performing an auto-test of a fullydischarged battery, such as a backup battery made of an Electricdouble-layer capacitor.

BACKGROUND

Nowadays, a plurality of electronic devices such as mobile phones,tablet PC or in general embedded devices use a backup battery which, asknown by a skilled man is a secondary power supply that provides powerto electronic devices in the absence of main power supplies. Inparticular, the backup battery is used to prevent losing sensitiveinformation when the device is no more supplied by a main power supply,such as, for instance, real time clock data.

Conventional batteries used for embodying backup batteries are based onNi-Cad and Lithium-Ion.

Also conventionally, electronic products manufacturers performproduction tests to ensure that any of the components of a productoperate properly after their assembly, and this also applies to theparticular backup battery included in the product.

The most common method for performing a production test is the visualmethod that carries out a visual test for detecting the presence of theproduct components. Such visual test can applied, either manually by ahuman person or automatically by using automated optical inspection.

In order to make the production tests more reliable and faster, thetrend is to involve more and more automation in production tests andthus generalizes the development of automated optical inspection appliedto the PCB (Printed Circuit Board) during the manufacturing process,e.g. by means of a camera capturing the PCB image from the side of thePCB where components are being assembled. The inspection machine scansthe PCB image in order to detect if all components are present and wellplaced.

Such method has been used also for checking the presence of the backupbattery. However, the visual method—be it manual or automatic—showslimitation since it is not appropriate to detect proper soldering of thecomponents or, even, proper working of the latter.

In order to further increase the reliability on checking thefunctionality of a product component as well as to decrease the durationof the testing process, more and more manufacturers integrate within theinternal circuits forming part of an electronic product a specificcircuit for achieving what is called auto-test (self-test) capability.

Accordingly, such electronic products have a capability to auto-test thefunctionalities of their components by themselves. In that respect, if abackup battery is included in one electronic product that supportsauto-test capability, its functionality can be tested automatically.

One known auto-testing technique for detecting the functionality of anelectronic product component and particularly of a backup battery, isthe performance of a voltage measurement, which is achieved by theinternal and General Purpose Analog-to-Digital Converter (GPADC) whichis generally present in recent power management unit (PMU).

Such conventional auto-test method is illustrated in FIG. 1, showing anelectronic product or appliance 10 which includes a Power ManagementUnit 20 to which is connected one battery 30, e.g. a backup battery 30.The Power Management unit 20 further includes a detecting block 40 whichsenses the voltage of the battery, plus a battery charger 50 and aGeneral Purpose ADC converter 60 having access to all analog voltagespresent in the circuit for the purpose of converting them into thedigital representation forwarded to a shown processor.

Particularly, GPADC 60 is used for measuring the voltage of the backupbattery 30 in order to check its presence.

a) Lithium-Ion or Ni-Cad backup batteries

The auto-test is traditionally applied to the Lithium-Ion and the Ni-Cadbattery since it allows to achieve very fast testing. Indeed,Lithium-Ion or Ni-Cad backup batteries are never fully discharged andthey have a minimum voltage guaranteed by the backup batterymanufacturer. Consequently, during the manufacture of an electronicproduct including a Lithium-Ion or Ni-Cad backup battery, the test of afully operative Lithium-Ion battery can simply be based on the checkingof the voltage generated by such battery without any preliminary need tocharge the latter. More particularly, if the measured backup batteryvoltage is between expected voltage thresholds the auto-test succeedsand thus the backup battery is presumed to properly operate and to bewell soldered. Otherwise the auto-test fails.

Therefore, auto-test process, when applied to Lithium-Ion and/or Ni-Cadbackup batteries, can be achieved in less than 1 ms.

b) Electric double-layer capacitors

The most recent of the above mentioned backup battery technologies isthe electric double-layer capacitor, also designated as being a GoldCapbackup battery. It includes an electrochemical capacitor that has anunusual high energy density compared to common capacitors. Also, itsmanufacture cost is less than Lithium-Ion and Ni-Cad backup batteries.

The problem lies on the fact that the known auto-test process describedabove cannot be achieved in less than 1 ms.

Indeed, as known by the skilled man, an electric double-layer capacitor,in contrast with the Lithium-Ion or Ni-Cad backup batteries, is alwaysdischarged and its voltage is 0V. Consequently, the checking of thepresence of a voltage on such a backup battery cannot directly andimmediately be performed, as for the Lithium-ion battery, just after thesoldering operation, since a preliminary charging operation of thebattery is required.

Such compulsory charging might take at least several hundreds ofmilliseconds, which would significantly impact the time formanufacturing the product and, eventually, jeopardize the productivity.

Indeed, considering for instance the flowchart of FIG. 2, there isdescribed the adaptation of the auto-test process—known to theLithium-Ion—for the new electric double-layer capacitor:

Phase I: initialization of the auto-test software;

Phase II: charging of the backup battery during a period sufficient forentailing a first increase of the voltage of the battery, e.g. at least500 ms;

Phase III: performance of voltage stabilization that lasts for ˜100 ms;

Phase IV: stop charging and measure the backup battery voltage, forinstance by means of the General Purpose ADC convertor.

At the end of phase IV, if the measured backup battery voltage shows tobe between the expected voltage thresholds the auto-test succeeds andthus the backup battery (in that case the electric double-layercapacitor) is presumed to be well soldered and operative. Otherwise, theauto-test fails.

The completion of the known auto-test process, when applied to thoseGoldCap batteries, required not less than 600 ms, which is significantlyhigher than the period required for testing Lithium-Ion and Ni-Cadbattery.

Therefore, the application of the conventional auto-test process of FIG.2 is not appropriate for electric double-layer capacitors or GoldCapbatteries since it requires too much time.

There is a wish for an alternative auto-test which is more adapted tothe new type of fully discharged backup batteries and which additionallyprovides more accurate test results.

SUMMARY

It is an object of the present invention to provide an auto-test processwhich is well adapted to fully discharged backup batteries—such aselectric double-layer capacitors.

It is another object of the present invention to provide an auto-testprocess requiring very short processing time even in the case ofelectric double-layer capacitors or batteries being fully dischargedwhen mounted and soldered on a PCB.

It is still a further object of the present invention to achieve anauto-test process which improves the accuracy of the auto-test by meansof checking more deeply the internal working of the battery.

It a still another object to achieve an auto-test of a backup batterywhich can still be used for more conventional Lithium-Ion or Ni-Cadbackup batteries.

These and other objects of the invention are achieved by a process forperforming an auto-test of a fully discharged battery, the processinvolving the steps of:

performing an initialization phase;

charging the backup battery with a predetermined constant current duringa predefined period allowing stabilization of said current (Icurrent);

detecting the voltage of the backup battery after the predefined period,when the battery is still being charged;

testing whether said sensed voltage is comprised within a predeterminedrange of threshold values, and

reporting a battery failure when said sensed value falls outside therange.

Preferably, the backup battery is a electric double-layer capacitor usedas a backup battery, and the process takes full advantage of the highimpedance of such battery for the purpose of producing a sensed voltagewhich can provide a clear information about the status of that battery.

Moreover, the testing can be performed in a very short period, forinstance less than 1 ms.

In one embodiment, the process is executed by a processor which receivesa digital representation of the sensed voltage by means of a GeneralPurpose Analog-to-Digital Converter.

In one embodiment, the GPADC is included into a Power Management Unit.

In one embodiment, the process can even be performed for the purpose oftesting more conventional backup batteries, such as Lithium-Ion orNickel Cad battery. In that case, the initialization phase isimmediately followed by a preliminary detection of the voltage of thebattery, prior to any charging, so as to generate a preliminary voltageVsoc. The test is then applied on the difference between the value ofthe voltage sensed after the predefined period (1 ms) and thepreliminary voltage Vsoc, so as to yield accurate information on theimpedance of the backup battery.

The invention also achieves a circuit for performing an auto-test of afully discharged battery of an electronic appliance including a batterycharger.

The circuit comprises:

-   -   means for performing an initialization phase;    -   means for charging the backup battery with a predetermined        constant current during a predefined period allowing        stabilization of the current (Icurrent);    -   means for detecting the voltage of said battery after said        predefined period, said battery being still in charge;    -   means for testing whether said sensed voltage is comprised        within a predetermined range of threshold values; and    -   means for reporting a battery failure when said sensed value is        outside said range.

Preferably, the backup battery is an electric double-layer capacitorused as a backup battery and the predefined period is set toapproximately 1 ms.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features of one or more embodiments of the invention will be bestunderstood by reference to the following detailed description when readin conjunction with the accompanying drawings.

FIG. 1 illustrates the prior art architecture of a product performingADC auto-test.

FIG. 2 illustrates the application of the conventional auto-test processon an electric double-layer capacitor.

FIG. 3 shows the architecture of a product performing auto-testaccording to the invention.

FIG. 4 illustrates a first embodiment of a process well suited to afully discharged backup battery.

FIG. 5 illustrates a second embodiment of a process which can also beused for more conventional Lithium-Ion and Ni-Cad batteries.

DETAILED DESCRIPTION

There will now be described one particular embodiment of a process whichis perfectly adapted to the more recent backup batteries which arebatteries showing full discharge after the manufacturing process.

More particularly, the description will be considered with the use of abackup battery being an electric double-layer capacitor; but clearly,the skilled man will adapt the process below to any other kind ofbatteries which are fully discharged when soldered or mounted on a PCB.More generally, it will be apparent to the skilled man that the processcan also be applied to any type of backup battery, including thewell-known Lithium-Ion and Ni-Cad, which can also take advantage of thehigher accuracy of the process which will be described below.

As recalled above, the electric double-layer capacitors are fullydischarged when manufactured and thus, a time period of charging andvoltage stabilization (at least 600 ms) would be required when applyingthe conventional auto-test process which is applied for Lithium-Ion.

The invention manages to significantly decrease the above mentionedcharging period to approximately 1 ms. This is achieved by takingadvantage of the very high internal impedance shown by the electricdouble-layer capacitors (˜100 Ohms) compared to more conventionalbatteries (e.g. Lithion-Ion and Ni-Cad batteries), such impedance beingmeasured directly after the start of a charging process, as describedhereinafter.

FIG. 3 shows the structure of an electronic product or appliance 110that incorporates one embodiment of the process described above.

The product 110 includes an electric double-layer capacitor 130 that isconnected to a Power Management Unit 120, the latter including a backupbattery charger 150, a detection block 140 and a General Purpose Analogto Digital Converter (GPADC) 160 for the measurement of the voltage ofthe electric double-layer capacitor 130.

It should be noticed that the PMU may take different forms and differentlevels of complexity. In some cases, the PMU may even incorporate aspecific process which will be used for the execution of the processsteps described below. Alternatively, the general purpose processorexisting in the appliance may be used for that purpose.

The product 110 further includes a detection block 170 connected to theelectric double layer capacitor 130 for the purpose of detecting thevalue of the voltage generated by said battery, which voltage isforwarded by means of appropriate wires (not shown in the figure) to theGPADC 160, so that to make such information available to the processor.

The backup voltage Vbackup is given by the following formula:

Vbackup(t)=Icharge(t)×Zbackup(t)+Vsoc(t)  (I)

where Vbackup(t) is a time function of the backup battery voltage;

Icharge(t) is a time function of the current that is provided by thebackup battery charger 150 and is considered to be constant, which isfor instance the case when charging is performed by a Constant CurrentConstant Voltage (CCCV) charging device. Indeed, as known by a skilledman a CCCV device performs both constant current charging and constantvoltage charging, but during two different consecutives periods. In afirst phase, the charging is performed with a constant current until thevalue of the backup battery reaches a predetermined value (e.g. 80% ofthe nominal value). Then, the CCCV charging device performs a constantvoltage charging and keeps that as long as its voltage is superior tosaid threshold, so as to keep the value of the backup battery close tothe nominal value. Clearly, this is one example of a charging devicewhich can be used, but any other arrangement can be considered.

Zbackup(t) represents a time function of the internal impedance of thebackup battery which, as mentioned above, shows a high value (typically100 ohms). and

Vsoc(t) is the State Of Charge of the backup battery and in particularVsoc(t) represents a time function of a backup battery voltage whenthere is no current drain through the latter. However, in the case ofthe electric double-layer capacitor 130 that is a fully dischargedbattery, Vsoc(t)=˜0V.

With respect to FIGS. 3, 4, 5 there is now described the basic steps ofthe process for performing an auto-test to the double-layer capacitor130 of the electronic product 110.

In a first step 210, the electronic product initializes the auto-test ofthe electric double-layer capacitor 130. During that step, the backupbattery charger 150 is switched off.

The process then proceeds to a step 220, wherein the backup batterycharger 150 is switched on so as to allow a current Icharge to flow fromthe latter to the electric double-layer capacitor 130 (see FIG. 3). Thecurrent Icharge is assumed to be constant.

Therefore, the charge of the electric double-layer capacitor 130 isstarted for a determined period which is chosen to ensure sufficientstabilization of both the current generated by the CCCV generator andthe voltage appearing at the terminals of the backup battery, when beingcharged.

It has been discovered, and this is one significant advantage of theprocess which is described, that 1 ms is sufficient for allowing bothestablishing of the charging current and an appropriate measurement ofthe voltage of the battery.

Clearly, the skilled man may select other values which, in any cases,are significantly lower than the 600 ms required in the conventionalauto-test process used for Lithium-Ion batteries.

Because of the high impedance (˜100 Ohms) of the electric double-layercapacitor, a non-negligible electric double-layer capacitor voltage(Vbackup) appears during the charging of the battery, which voltage canbe sensed, in a step 230, by means of detection block 170 and alsoforwarded to the General Purpose Analog to Digital Converter 160 so asto be processed by an appropriate processor, be it the general purposeprocessor present in the appliance or, alternatively, the specificprocessor existing in the Power Management Unit 120.

GPADC converter 160 thus generates a digital representation of theanalog voltage sensed on the backup battery, which is:

Vbackup=Icharge×Zbackup+Vsoc(t)

As mentioned above, since the battery is assumed to be discharged, thenVsoc is 0V, so that the knowledge of Vbackup directly gives anestimation of the value of Zbackup, since the value of Icharge is known.

Then the process proceeds to a step 240, wherein a test is performed oneither the value of the impedance or, more directly, on the value ofVbackup so as to determine whether the latter is comprised between twopredetermined threshold values V1 and V2.

Generally speaking, the predetermined voltage values V1 and V2 arechosen by taking into consideration the sum of inaccurate parameters inthe measurement path. Eg:

-   -   Charge current inaccuracy (% Icharge);    -   Backup battery impedance inaccuracy (% Zbackup);    -   Analog to Digital Converter measurement inaccuracy.

If Vbackup is comprised between the predetermined voltage values V1 andV2, then the process proceeds to a step 250 wherein the auto-testreports a successful test.

In that case, the electric double-layer capacitor is presumed to workproperly and it is well soldered.

Otherwise, if the value of Vbackup shows to be not comprised between thepredetermined values V1 and V2, the process proceeds to a step 260wherein the auto-test reports a battery failure.

In that case, the electric double-layer capacitor does not work properlyand/or is not well soldered.

Particularly, if Vbackup is too high it means that the battery is eitherold or even, if Vbackup is equal to the power supply voltage, that nobattery is present on the PCB.

With respect to FIG. 5, there will now be described a second embodimentof a process which can even be used for testing the more conventionalLithium-Ion or Ni-Cad batteries.

In a first step 310, the process proceeds with an initialization step.During that step, the backup battery charger 150 is switched off.

Then the process proceeds to a step 320 where a first detection of thevoltage of the backup battery is being performed, so as to determine thevalue of Vsoc, without any current being drawn or injected within saidbattery.

Then the process proceeds to a step 330, wherein the backup batterycharger 150 is switched on and a constant Icharge current is flown intothe battery during a period which can be set, in one preferredembodiment, to a duration of approximately, to 1 ms.

After said period of 1 ms, the process then proceeds to a step 340 wherethe voltage value of the backup battery is sensed again, but still whilebeing charged. The GPADC generates the digital representation andforwards the latter to the processor which can then perform, whenappropriate, the computation of the impedance of the Lithium-Ion orNi-Cad battery at step 370.

Then the process proceeds to a step 350, wherein a test is performed onthe value of (Vbackup—Vsoc) (the former being sensed in step 340 whilethe latter was sensed in step 320), so as determine whether thatdifference is comprised between two predetermined threshold values V_(A)and V_(B). The particular values of V_(A) and V_(B) will be determinedby the skilled man by taking into consideration various parameters, suchas those mentioned above.

If (Vbackup−Vsoc) is comprised between the predetermined voltage valuesV_(A) and V_(B), then the process proceeds to a step 360 for reporting asuccessful auto-test. Conversely, the process reports a failure or a notpresent battery.

In the embodiments which were described above, the tests of step 240 and340 are clearly performed by means of the processor which also executesthe process described above. However, it should be clear that theskilled man may also perform the steps 240 and 340 by means of analogcircuits, particularly operational amplifiers, wired for the purpose ofperforming the comparison with the thresholds values V1, V2, V_(A) andV_(B).

What is claimed is:
 1. A method of auto-testing a fully dischargedbattery of an electronic appliance that includes a battery charger,comprising: configuring a circuit to test any one of a lithium-ion,nickel-cadmium, and electric double-layer capacitor type battery used inan electric appliance; performing an initialization phase; charging thebattery with a predetermined constant current during a predefined periodhaving a duration that allows stabilization of the current; detecting avoltage of the battery after the predefined period, while the battery isstill being charged; determining whether the detected voltage is withina predetermined voltage range; and reporting a battery failureresponsive to the detected voltage being outside the predeterminedvoltage range.
 2. The method of claim 1, wherein the electronicappliance also includes a processor, and a General PurposeAnalog-to-Digital Converter (GPADC) configured to convert the detectedvoltage into a digital signal and transmit the digital signal to theprocessor.
 3. The method of claim 1, wherein the GPADC is part of aPower Management Unit of the electronic appliance.
 4. The method ofclaim 1, wherein the predefined period is approximately 1 millisecond.5. The method of claim 1, further comprising: reporting that the batteryis absent responsive to the detected voltage being equal to a voltage ofa power supply of the electronic appliance.
 6. The method of claim 1,wherein the detected voltage is calculated as:Icharge(t)×Zbackup(t)+Vsoc(t), where Icharge(t) is the current at timet, Zbackup(t) is the internal impedance of the backup battery at time t,and Vsoc(t) is the state of charge of the battery at time t.
 7. Themethod of claim 1, wherein detecting the voltage of the battery afterthe predefined period is performed by a detection circuit in theelectronic appliance.
 8. The method of claim 1, wherein the methodfurther comprises: detecting a preliminary voltage of the battery afterthe initialization phase but before the charging has begun.
 9. Themethod of claim 8, wherein the method further comprises: subtracting thepreliminary voltage from the detected voltage prior to the determiningto obtain an adjusted voltage, such that the determining comprisesdetermining whether the adjusted detected voltage is within thepredetermined voltage range, and the reporting comprises reporting abattery failure responsive to the adjusted detected voltage beingoutside the predetermined voltage range.
 10. The method of claim 1,wherein the charging the battery during a predefined period having aduration that allows stabilization of the current, also allowsstabilization of the voltage.
 11. A circuit for auto-testing a fullydischarged battery of an electronic appliance that includes a batterycharger, the circuit being configured to: test any one of a lithium-ion,nickel-cadmium, and electric double-layer capacitor type battery used inan electric appliance; perform an initialization phase; charge thebattery with a predetermined constant current during a predefined periodhaving a duration that allows stabilization of the current; detect avoltage of the battery after the predefined period, while the battery isstill being charged; determine whether the detected voltage is within apredetermined voltage range; and report a battery failure responsive tothe detected voltage being outside the predetermined voltage range. 12.The circuit of claim 11, wherein the appliance includes a processor, anda General Purpose Analog-to-Digital Converter (GPADC) configured toconvert the sensed voltage into a digital signal and transmit thedigital signal to the processor.
 13. The circuit of claim 11, whereinthe GPADC is part of a Power Management Unit of the electronicappliance.
 14. The circuit of claim 11, wherein the predefined period isapproximately 1 millisecond.
 15. The circuit of claim 11, wherein thecircuit is further configured to: report that the battery is absentresponsive to the detected voltage being equal to a voltage of a powersupply of the electronic appliance.
 16. The circuit of claim 11, whereinthe detected voltage is calculated as:Icharge(t)×Zbackup(t)+Vsoc(t), where Icharge(t) is the current at timet, Zbackup(t) is the internal impedance of the backup battery at time t,and Vsoc(t) is the state of charge of the battery at time t.
 17. Thecircuit of claim 11, wherein a detection circuit for detection of thevoltage of the battery is in the electronic appliance.
 18. The circuitof claim 11, wherein the circuit is further configured to: detect apreliminary voltage of the battery after the initialization phase butbefore the charging has begun.
 19. The circuit of claim 18, wherein thecircuit is further configured to: subtract the preliminary voltage fromthe detected voltage prior to the determining to obtain an adjustedvoltage, such that the determining comprises determining whether theadjusted detected voltage is within the predetermined voltage range, andthe reporting comprises reporting a battery failure responsive to theadjusted detected voltage being outside the predetermined voltage range.20. A circuit for auto-testing a fully discharged battery of anelectronic appliance that includes a battery charger, the circuit beingconfigured to: perform an initialization phase; charge the battery witha predetermined constant current during a predefined period having aduration that allows stabilization of the current; detect a voltage ofthe battery after the predefined period, using a detection circuit inthe electronic appliance, while the battery is still being charged;determine whether the detected voltage is within a predetermined voltagerange; and report a battery failure responsive to the detected voltagebeing outside the predetermined voltage range.